1. Field of the Invention
This invention relates to a protective breathing apparatus, specifically, it relates to valves for use with gas masks and respirators.
2. Description of the Prior Art
In many gas masks and respirators, valves are used to direct the flow of air caused by breathing of the user from an intake port and out an exhalation port. In order to reduce the hardship of wearing these protective devices, it is desirable that the valves used be reliable and that they operate on minimum pressure differentials. The pressure to open the exahalation valve has been found to be directly related to the comfort of a wearer, the lowest possible opening pressure being desired. Further, it is both desirable and a safety code requirement that the exhalation valve be completely closed at its rest position. These two requirements are not entirely compatible as a valve that is closed in the rest position tends to be harder to open than one which does not fully close. In general, such valves take the form of a more or less rigid seat and a rubber flap valve cooperating therewith. In the more refined valves, the valve is a disc fastened at its center to the valve seat.
Gas mask and respirator valves are often required to operate in atmospheres of extremely high humidity and they may become covered with condensed moisture. The effect of moisture on a valve is to make it more difficult to open. This is particularly true of valves having an extensive seat area.
Numerous valves are known having designs directed toward the goal of complete closure and minimum opening pressure. One such design embodies a seat having a plurality of seating ridges with valleys in between. In another valve, the valve is molded with a dependent skirt contacting a flat valve seat. Valves are known having curved valve seats. With such valves, it has often been the practice to use a molded valve shaped to conform closely to the seat. In all these valve designs, it has been found that moisture can cause a considerable increase in the opening pressure. This is because in such designs there is a considerable area where water can lodge and hold the valve to the seat by capillary forces.